One of the methods available for upgrading between 8.3x to 9.1 is the Automated Nondisuptive Upgrade (ANDU) method. This method simplifies the upgrade process and removes much of the burden of the process. There still remains a few items that need to be reviewed and performed prior to using the ANDU method. Following is an outline of the manual checks that the ANDU requires. For the complete documentation on the process use the Upgrade Express Guide.

tl-dr ( how do I upgrade ONTAP when clusters are both a source and a destination for SnapMirrors. Instructions say destination first. Whaaa? )

We are planning upgrade from 8.3.1 to 9.1P5 . The AutoSupportUpgrade Advisor Plangenerated for this task, gives the following advice for suspending SnapMirror replication, and the correct order in which to upgrade the Peers of the SnapMirror relationship:

Suspending SnapMirror operations

WARNING

Cluster mycluster2 is running SnapMirror.

To prevent SnapMirror transfers from failing, you must suspend SnapMirror operations and upgrade destination nodes before upgrading source nodes.

(i) Suspend SnapMirror transfers for a destination volume

(ii) Upgrade the node that contains the destination volume

(iii) Upgrade the node that contains the source volume

(iv) Resume the SnapMirror transfers for the destination volume.

Note: SnapMirror transfers for all other destination volumes can continue while the nodes that contain the original destination and source volumes are upgraded.

Our problem is that mycluster2 and the Cluster it is SnapMirroring to, mycluster1 have Volumes where SnapMirror replication is going in both directions:

That certainly makes a tough decision. As you have it you would need to suspend SnapMirrors originating from the cluster you upgrade first. The alternative though to this problem is configuring version-flexible SnapMirror relationships. That is described starting on page 99 here:

Thanks for the tip Amandeep. I 'm not running any Snapmirroring on this filer at the moment and to be honest disabling deswizzle is not something I did in the past before an OS upgrade. Unless if things have changed with the latest CDOT versions.